SkyOS has always been criticised for the fact that you have to pay for it in order to beta test it. I personally never saw a problem with this construction, especially since the price included a full copy of SkyOS 5 (they dropped the five) once it was completed. However, as of late, it has become increasingly clear that there may never be anything like a final version - or another test release for that matter. Update: In the comments, Robert Szeleney explained the current SkyOS situation in more detail. For future readers who find this article via a search engine, I've attached Robert's comment to the actual story for completeness' sake. The reply can also be found on the SkyOS website.

He is developing SkyOS 5 for 6 years now. What makes you think he will ever finish it?

Well when is Linux "finished"? Its been in development for 16 years.
If SkyOS would be released now in many aspects it would be more modern than Windows and Linux today. (Sadly with less drivers)
And its better to be closed as to be open and a mess.

Why not go to DistroWatch and look for a distro labeled "stable" or "final" and not a beta release? There's no shortage of them. Meanwhile, the kernel itself is on a schedule which releases a "stable" version regularly.

I think you're confusing the words "finished" (as in completely done; nothing left to do) with "ready for use." And software never gets truly finished in that way, since even the most "complete" software will start to show limitations eventually. "Finished" in the context that it was used simply means ready for use by more than just beta testers.